Social Media Claim
Fort Denison pics no indicator of sea level rise
A Facebook post from June 1, 2019 shows two photos of Fort Denison and claims there has been no sea level rise in Sydney Harbour.
AAP FactCheck examined a Facebook post shared on October 11, 2019 by AUSTRALIA-The Land Down-Under which shows two photographs of Fort Denison in Sydney Harbour. The post claims them as evidence there has been no rise in sea level in Sydney Harbour 140 years.
The post shows the two pictures side by side, one in black and white, with text at the top reading, “unprecedented climate change has caused sea level at Sydney Harbour to rise approximately 0.0cm over the past 140 years”.
Fort Dension sits on an island in Sydney Harbour that was a detention location before work began in 1840 on construction of the stone building.
The first photo of Fort Denison was taken prior to 1885, according to the State Library of NSW, which has the original image in its archives. The distinctive tower structure on the island was completed in 1857. The Bureau of Meteorology has sea level reading records dating back to 1914 for Fort Denison.
AAP FactCheck was unable to find the origin of the second photo but the naval ship in the background bears the number 304, which is the identifier for Australian navy ship HMAS Success. The HMAS Success was in service from 1984 until June 2019.
AAP FactCheck was unable to verify if the images were taken 140 years apart. However, according to the timelines of Fort Denison’s construction and the launch of the HMAS Success, the photo were taken between 99 years and 162 years apart.
A spokesperson for the Australian Bureau of Meteorology (BOM) said sea levels have risen by between about 68mm and 105mm in Sydney Harbour between 1914 and 2007.
“Global rates of change range from 1.4 mm/yr (between 1901 and 1990) to 3.2 mm/yr (between 1970 and 2015), while estimates of sea level rise within Sydney Harbour range from 0.73 - 1.13 mm/yr (between 1914 and 2007), slightly less than the global average,” the spokesperson said.
The data referenced by the BOM spokesperson is from a 2009 study commissioned by the NSW Department of Environment.
Regarding the photographs used in the post, the BOM spokesperson said using the images to determine a change in sea level would be impossible.
“Sea level varies throughout the day and year due to the influence of tides and seasonal shifts in weather systems,” the spokesperson said.
“Just as two single photographs of equivalent sea level, at a particular location, do not tell us whether the tide is coming in or going out, two single photographs from a location taken many years apart do not inform whether sea level is rising or falling over that period.
“A good analogy for this is that we don't find a picture of a hot summer’s day from 1950, and a picture from a cold winter’s day in 2010, and infer that there has been no warming trend over that time.”
Based on the above evidence, AAP FactCheck found the post claiming there had been no sea level rise in Sydney Harbour over the past 140 years to be false.
- False - The primary claim of the content is factually inaccurate.
First published October 25, 2019, 15:25 AEST